Traditionally, carburetors are used in combustion engines using fuel such as gasoline as devices to cause fuel to be atomized and mixed with air. Normally, a pilot outlet hole is formed in a carburetor and opening area thereof is adjusted by screwing the pilot screw, so that quantity of fuel to be mixed with air can be adjusted. That is, when the opening area of the pilot outlet hole is reduced by screwing-in the pilot screw, quantity of fuel in mixture can be reduced. On the other hand, when the opening area of the pilot outlet hole is increased by releasing the pilot screw, quantity of fuel in the mixture can be increased.
Here, when the opening area of the pilot outlet hole is adjustable without limitation, there may be a case that exhaust gas after gasoline is combusted exceeds predetermined regulation values. In order to make the opening area of the pilot outlet hole adjustable only within the exhaust gas regulation, it is required to regulate adjustment angle (rotatable range) of the pilot screw.
Conventionally, a tamper cap has been arranged at a pilot screw as means for regulating adjustment angle of the pilot screw (for example, see Patent Literature 1). Here, when the tamper cap is rotated, a projection portion of the tamper cap is stopped by a stopper member of a carburetor body. Accordingly, the adjustment angle of the pilot screw which is rotated in synchronization with the tamper cap is regulated into a predetermined range.
In a case of using a tamper cap, to reliably meet the exhaust gas regulation, the tamper cap is required not to easily drop as being fixed to the pilot screw. In most cases of the related art including Patent Literature 1, resin-made tamper caps have been used. With a resin-made tamper cap, the tamper cap is easily broken when an excessive force is applied. In this case, there has been a possibility that the pilot screw becomes rotatable without limitation.
Meanwhile, metal-made tamper caps have been proposed. When a metal-made tamper cap is used, glue is generally used as fixing means for a pilot screw. In a case that a tamper cap is made of metal, there is an advantage that risk of being broken by an excessive force is reduced compared to a resin-made tamper cap.
That is, non-destructivity of the metal-made tamper cap is improved compared to a resin-made tamper cap. However, there has been a problem that the tamper cap drops from the pilot screw causing the pilot screw to be in a state of being rotatable without limitation when an excessive force more than bonding strength of glue is applied. In addition, there has been a problem that the tamper cap drops from the pilot cap due to poor bonding or time degradation.
Besides the structure using a tamper cap, the related art includes a structure that a hole plug is arranged for a pilot screw. However, the structure with a hole plug has a disadvantage that a pilot screw cannot be adjusted at all.